Project Summary Highly successful prevention of mother-to-child transmission (PMTCT) programs have reduced the number of infants acquiring HIV from their mothers. In 2013 there were 1.3 million women living with HIV who gave birth to 199,000 HIV-infected and approximately 1 million HIV-exposed, uninfected (HEU) infants. In South Africa, where a 30% infection rate is reported among pregnant women at antenatal clinics, the HIV epidemic continues to be a significant public health burden on women and children. Maternal HIV infection may disrupt normal development of the infant gut microbiome, affecting the development of the immune system and contributing to the higher morbidity and mortality of HEU infants. In addition, since microbiota influence communication between the gut and the brain, changes in the infant gut microbiota related to maternal HIV infection may help to explain the delayed neurodevelopment sometimes observed in HEU infants. This proposal builds on the infrastructure and data of a recently funded study designed to measure the effects of in utero and perinatal exposure to ART and HIV on the developing infant brain. The existing study follows 210 infants, 140 HEU and 70 HU. At 38 to 41 weeks gestational age (GA), the infants will undergo neuroimaging, including structural imaging for brain morphometry, diffusion for brain connectivity, and spectroscopy for brain metabolism, and neurodevelopmental assessments at 9 and 19 months of age. This proposal seeks to expand the current study, adding an additional neuroimaging time point (at 12 months), infant gut and maternal breast milk microbiome measures and breast milk oligosaccharide composition. We will acquire infant gut microbiome samples at 5-7 days, 3 and 12 months. In addition, breast milk samples will be acquired at 5-7 days and 3 months for microbiome analysis, and human milk oligosaccharides (HMO) composition analysis at the first two time points. We hypothesize that abnormalities identified in neuroimaging measures in HEU infants will be related to reduced gut microbiome diversity. The goals of this study are to describe the maturation of the infant brain and gut microbiome composition, and to examine the relationship between maternal breast milk HMO and microbiome composition, gut microbiome diversity and neuroimaging measures. We seek to identify differences related to maternal HIV-infection that will provide insight into increased risks of HEU infants and reveal potential areas for targeted intervention to improve health and neurodevelopmental outcomes. This project extends the existing collaboration between Drs van der Kouwe (Massachusetts General Hospital), Meintjes (University of Cape Town (UCT)) and Laughton (Stellenbosch University), to include Dr. Lars Bode from University of San Diego who is an expert in HMO composition, as well as three UCT-based early stage investigators, Drs Holmes, Kaba and Robertson. The study aims to expand and strengthen local capacity and interdisciplinary collaboration focused on locally relevant health problems.